WASHINGTON — A genetic mutation that raises the risk of breast cancer is found in up to 60% of U.S. women, researchers reported Sunday.
Reports from several teams around the world identified changes in four genes that significantly raise the risk of breast cancer. Several are found in many men and women.
More than 60% of the women in the United States probably carry at least one of the mutations in one of the genes, called FGFR2, the researchers said.
"This is a truly landmark breakthrough for breast cancer research, because these genes are the first confirmed common genetic risk factors for breast cancer," said Jianjun Liu of the Genome Institute of Singapore, who took part in one of the studies.
The researchers, reporting in the journals Nature and Nature Genetics, said the discoveries were the most important genes associated with breast cancer since BRCA1 and BRCA2 were identified.
Women with faulty copies of those genes have a 50% to 85% chance of getting breast cancer in their lifetimes. But they are rare genes, and account for less than 10% of breast cancer cases.
Researchers have been testing women for other genes associated with breast cancer, to find its causes, to understand how and why it develops, and to make more effective treatments.
David Hunter of Harvard University and a team at the U.S. National Cancer Institute looked at more than 2,200 women of European ancestry.
They found four common mutations in FGFR2 associated with breast cancer in post-menopausal women who did not have known relatives with breast cancer.
The mutations raise the risk of breast cancer by 20 percentage points if they carry one copy of the gene and by 60 percentage points if they carry two copies. Close to 60% of the women they studied carried at least one copy.
However, Hunter said, "it is premature to recommend screening women for these gene variants" until scientists have found "all the variants that are associated with increased risk."
Douglas Easton of Britain's University of Cambridge led a team of researchers around the world to look at tiny changes in a code in the DNA of about 21,800 people with breast cancer and about 22,600 without it.
They found mutations in four genes that were more common in the people with breast cancer -- FGFR2, TNRC9, MAP3K1 and LSP1.
FGFR2 may be a logical candidate for a breast cancer gene because it serves as a kind of molecular doorway for a compound involved in several cancers.
In a third study, a team from biopharmaceutical company deCODE Genetics, the University of Nijmegen in the Netherlands and elsewhere studied 22,000 people to find two other gene mutations associated with breast cancer. One is also near TNRC9.
The company said it estimated these mutations were "contributing factors" in 25% of breast cancer cases in women of European ancestry.